Manufacture of diazotype sensitive papers and the like



July 8, 1930. H. D. MURRAY 1,770,352

MANUFACTURE OF DIAZOTYPE SENSITIVE PAPERS AND THE LIKE Filed Sept. 28, 1929 TTORNEYS.

Patented July 8, 1930 UNITED STATES PATENT 'or-'rice HUMPHBEY DES'MOND MURRAY, OF SOUTH KENSINGTON, LONDON, ENGI'JAND, AS- SIGNOR OF ONE-HALF T NORTON .AND GREGORY LIMITED, OF LONDON, ENGLAND MANUFACTURE OF DIAZOTYPE SENSITIVE PAPERS A ND THE LIKE No Drawing. Application led September28, 1929,. Serial No. 395,989, and in Great Britain June 14, 1928.

The present invention is for improvements in or relating to the production of photographic images by the diazo-type process, and has particular reference to the manufacture of improved sensitive papers, or other hydrophilic bases, for application in this art.

In brief, the diazo-type process consists 1n exposing a light-sensitive diazo-compound on a suitable supporting medium, such as paper,

to light beneath a design, whereby the said compound is decomposed where unprotected by the outlines of the design, and the povver of combining with an azo-dyestuff coupling component is destroyed. After the exposure,

the surface is treated with a suitable solution of a couplin component, or, Whensaid component has een an original co-mgredient with the .diazo-compound on the paper or other support, with 'an alkali, so that a replica of the original tracing is vobtained as a coloured dye image on a more or less white ground.

When coupling solutions are employed, they usually contain a non -volatile alkali, and asdye image prints are seldom washed with Water, an excess of this alkali and of coupllng component remains on the surface of the dye image print. After some time, according to the circumstances and the nature of the compounds employed, the background of such prints discolours, possibly in consequence of the oxidation of the excess of coupling comonent in the presence of the non-volatile al- *ali. Such alkali may be used to promote coupling when the diazo-compound and coupling component therefor are present together on the base, and the same disadvantage tends to arise.

This -darkening can be greatly retarded by removing the excess of said alkali in the surface of the paper or like support by the application of a solution of an acid after the development, but Withcertain combinations of diazo-compounds and coupling components, the application of such acid solution modifies the normal colour of the dye image.

The present invention concerns that form of the diazo-type photographic process wherein development is effected by aid of a 50 solution of non-voltatile alkali, the use of which, as just stated, tends to result in subsequent deterioration of the print. The invention is therefore particularly applicable to a process in which diazo-compounds are employed which couple readily only in definitely alkaline solution.

The invention may be best understood by reference `to the accompanying'drawing in which Figures 1 to 4, inclusive, are enlarged sectional views of sensitized papers, manufactured in accordance with the principles of the present invention, the four views illustrating four different modifications of the invention.

According to this invention, the manufacture of papers or the like for the diazo-type process is characterized by combining With the paper or the like discretely from the sensitizing substance a neutralizing agent for non-volatile alkali.

Thus, the Asaid neutralizingagent may be incorporated in the paper or like supporting material vat the time of preparation of such aper or material as illustrated in Figure l.

this modification of the process being illustrated in Figure 3 of the drawing.

In alternative, as illustrated in Figure 2,

the said neutralizing agent may be coated on one side of the supportingmaterial, for example, by applying a solution of the agent to one side of a thin, absorbent paper, the other side of which is coated with the diazo-compound, with or Without an azo-coupling component as may be desired.

A. second alternative is to coat the support-- ing material With4 the said neutralizing agent in the form of a solution with a Water-soluble colloidsuch as gelatine, and then to apply to the colloidv surface the coating of the diazocompound, alone or in conjunction with' an azo-coupling component as shown in Figure 4.

Or again, the surface of the supporting material may be treated with the neutralizing agent, a gelatine or like coating overlaid upon the so treated surface, and the diazocompound applied over all with or without an azo-couplmg comdponent, this modification being also illustrate in Figure 3 of the drawing. In this case, the diazo-compound may be advantageously applied in some solvent in which the neutralizing agent is only sparingly soluble. For example, a supporting base .impregnated with ammonium chloride may be coated with the diazo-compound in alcoholic solution.

It is well known practice in the art to prepare diazotype papers and like bases with sensitizing solutions containing an acid, and no claim is made herein to such manufacturing per se. According to the present invention, the supporting base of paper or the like carries distinct from the sensitizing layer and apart from any acid contained therein a neutralizing agent for non-volatile alkali. In the preferred embodiment of this invention, the supporting base carries more acid than is conta-ined in the sensitized surface. This excess of acid (or equivalent neutralizing agent for non-volatile alkali) produces its e'ect only when the base has been made sufficiently moist during development to permit of diffusion of the acid or the like; whereas acid accompanying the diazocompound does not function in such manner, because neutralization must take place before the associated diazo-compound can couple. There is likewise no broad claim made herein to the impregnation of paper or the like with acids, but solely to such impregnation for the manufacture of diazotype apers and the like as and for the purpose escribed.

The application of an alkaline solution to the side of the supporting material which carries the diazo-compound results irst in effecting the combination of this compound with the coupling component, either present with the said compound upon the surface of the supporting material, or dissolved in the alkali solution; and then as the said solution penetrates the surface of the supporting material or gelatine layer and reaches the neutralizing agent, the diffusion of such neutralizing agent as is dissolved in the solution results in the destruction of the free alkali, so that when dried, the surface of the supporting material is non-alkaline or acid, a

condition which, as aforesaid, inhibits dis-y colouration b oxidation.

The neutra izing agent for the non-volatile alkali may be an acid or an acid salt, but of not too corrosive a nature as adversely to affect the supporting material in a reasonable time; or an ammonium salt may be employed. Solid organic acids represent the type of acid most conveniently utilizable. One preferred acid of this class is oxalic acid, and a 5 per cent solution thereof has been found both convenient and effective for any of the methods of application already described. Ammonium chloride is both a convenient and satisfactory salt of ammonium to employ as neutralizing agent; and potassium bioxalate and sodium hydrogen tartrate are examples of suitable acid salts.

When an aqueous solution containing a fixed alkali, suchas sodium hydroxide, or a substance, such as sodium biborate which gives an alkaline reaction when dissolved in water, is applied to a supporting base containing an ammonium salt such as ammonium chloride, reaction takes place between the alkali (hydroxyl ions) in solution and the ammonium salt (ammonium ions) in the paper. Ammonium hydroxide is formed which breaks down into water and ammonia gas, vand the latter escapes from the surface of the supporting base, the alkalinity of which is reduced in the same way as if a portion of the alkali in the solution had been neutralized by acids. As the paper dries, all the ammonia gas set free leaves the paper, and the reaction of the latter approaches neutrality or, especially if the alkalinity of the applied solution has been produced by hydrolysis as aforesaid, becomes definitely acid.

Example I A hard surface paper is coated with an aqueous solution containing 1% of gelatine and 4% of oxalic acid, and dried. There is then applied a mixture of a light-sensitive diazonum compound andoxalic acid (1% of the mixture) and the paper again dried. After exposure to light beneath the desired design, development is effected with a solution containing 1.0 part Q-naphtholsulphonic acid.

8.0 parts sodium carbonate.

100.0 parts water.

Example I I Lused in the` appended claims is intended to include any suitable base of a porous material such as may be used in the art to which this invention relates.

Claims:

l. A diazo-type sensitized paper having a light sensitized layer, said paper being impregnated discretely-rom said layer with a neutralizing agent for non-volatile alkali.

2. A diazo-type sensitized paper having a surface coating of a lightsensitive diazocompound in a mixture with a Water soluble colloid, said paper being impregnated discretely from said layer with a neutralizing agent for non-volatile alkali.

3. A diazo-type sensitized paper having a surface coating of a light sensitive diazocompound in admixture With a Water soluble colloid, the oppositesurface of said Paper being impregnated with a neutralizing agent for non-volatile alkali.

4. A diazo-type sensitized paper having a surface coated with a Water miscible co1- loid and having a light sensitive diazo-compound upon the coating, said paper being partially impregnated discretely from said layer with a neutralizing agent for non-volatile alkali.

5. A diazo-type sensitized paper having a light sensitized layer, and bearing separately and discretely therefrom a neutralizing agent for non-volatile alkal'.

HUMPHREY DESMOND MURRAY. 

